Recent years have seen significant progress in the field of white-light emitters, which include a phosphor illuminated by at least one blue light emitting diode.
Some white-light emitters are configured so that the phosphor or a phosphor layer directly contacts the LED die. There are potential drawbacks to such a configuration. For instance, the photon density may be relatively high and may saturate the phosphor. In addition, the LED may be relatively hot, and the high heat may darken the phosphors over time and reduce the efficiency of the device.
For these and other reasons, a different configuration has become favored in particular applications, where the phosphor is physically separated from the LED die. This configuration is known as including a “remote” phosphor. The remote phosphor is physically spaced from the LED die, leading advantageously to a reduction in photon density and a reduction in heat exposure for the phosphor.
Some remote phosphor configurations use an extruded plastic pre-form, typically made from clear polypropylene or polyethylene that includes the phosphor. These extruded forms may be formed into generally convenient shapes, such as the exterior lens of a light fixture. However, there are several disadvantages to use of an extruded element.
For instance, the extrusion process gives a part-to-part variation in color temperature that may be unacceptably large. For instance, in some cases the variation in color temperature from part-to-part may be as large as +/−500K. Use of these extruded parts, with such a large part-to-part variation in color temperature, may require sorting and binning of the parts in order to meet an overall color temperature tolerance for a device, which is undesirable. Another potential disadvantage is that the extrusion process requires the running of relatively large amounts of material, even if only small amounts are needed. Still another potential disadvantage is that the extrusion process may require relatively complicated equipment for compounding, which blends the phosphor into a plastic base material.
For at least these reasons, it would be desirable to have a remote phosphor element formed from a process other than extrusion.